Path of the Primordial's Fury

You call upon the power of you primordial ancestors to enhance your rage and increase your already overwhelming power. This subclass is designed for those descended from efreeti but could be adapted for any primordial. 

Burning Fury

Starting at Level 3, your soul burns hotter while you rage than your body is used to and begins to properly boil your blood and blister your skin. While you are raging, at the start of each of your turns you and all creatures within 10 ft of you take fire damage equal to half your barbarian level rounded up. In addition, your melee weapon attacks deal an extra 1d6 fire damage. 

Beginning at Level 10, you can control the heat emanating from your soul. You can now choose which creatures take the fire damage at the start of your turn.

Obsidian Skin

Starting at Level 6, your skin begins to harden like stone even when outside of your rage. You are no longer effected by extreme heat as described in the DMG. In addition, once per short rest, you can use your reaction when taking bludgeoning, piercing, or slashing damage to gain resistance to those damage types until the the start of your next turn. If you are raging, this becomes immunity, but only to this one instance of damage.

Efreeti's Form

Starting at 10th level, while raging your primordial form more closely resembles the Efreeti youre descended from. In addition, while in this form you can turn your legs into a gas like proper genies and you gain a 30ft fly speed for the duration of your rage. 

Genie's Soul

Starting at 14th level, once per long rest you can enhance your rage and spread it to others. For the duration of your rage, you can grant 3 creatures you can see within 30ft of you resistance to fire damage. In addition, during this rage you lose most all human qualities about yourself and become more like an Efreeti in body and soul. Your fly speed increases to 60ft, you deal 2d6 extra fire damage instead of 1d6, your unarmed strikes deal 1d8 magical bludgeoning damage, and your resistance to fire becomes an immunity.